The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. It specifies a complete network system including the radio access network (UMTS Terrestrial Radio Access Network (UTRAN). The fourth generation (4G) mobile cellular system, also called the Long Term Evolution (LTE) (or 4G LTE) standard, now has a Release 12 that provides a way for User Equipment (UE) to be connected to two Evolved UTRAN (E-UTRAN) NodeBs (eNBs) at the same time using “Dual Connectivity” (DC). An eNB is the hardware that is connected to the mobile phone network that communicates directly with mobile handsets (UEs), like a base transceiver station (BTS) in Global System for Mobile Communications (GSM) networks. In LTE DC, there is a Master eNB (MeNB) that maintains the Radio Resource Control (RRC) connection with the UE and there is a Secondary eNB (SeNB) without RRC. The user data traffic flows via both the Master and the Secondary (thus justifying the name “dual connectivity”).
The problem with LTE DC is that it does not take advantage of other existing wireless network services such as Wi-Fi®. On the contrary, LTE has been extended with a proposal for the use of the LTE radio communications technology in unlicensed spectrum, such as the 5 GHz band used by dual-band Wi-Fi equipment. Wi-Fi as used herein refers to any “wireless local area network” (WLAN) product based on IEEE 802.11 standards. The term License Assisted Access (LAA) has been used to describe this development and a workshop has been established to share ideas in LAA-LTE. The study, however, mainly focused on co-existence between LTE and Wi-Fi. For example, some 3GPP and 4G vendors proposed time-division multiplexing between LTE and Wi-Fi to share the same unlicensed spectrum. This is not an efficient use of existing Wi-Fi infrastructures or an efficient integration of LTE and Wi-Fi.